Discontinuous reception (DRX) is a method used in communication networks to conserve battery energy of terminal devices, e.g., mobile devices or user equipments (UE). The UE and the network negotiate phases in which data transfer happens. During other times the device turns its receiver off and enters into a low-power state. On the other hand, discontinuous transmission (DTX) is a method of momentarily powering-down, or muting, a terminal device, e.g., a mobile or portable terminal, when there is no input data to the terminal device. This optimizes the overall efficiency of a wireless voice communications system.
One major aspect affecting the UE stand-by time is the possibility to inactivate the UE receiver circuitry. In the Universal Mobile Telecommunications System (UMTS) Radio Access Network (UTRAN), this is mainly utilized in paging states, where the UE is listening periodically to the paging channel. DRX period(s) and triggers/timers which result in DRX are typically configured by Radio Resource Control (RRC) functionality. Alternatively, the network may direct inactive UEs to DRX by explicit commands. Configuring long DRX periods allows for long standby times with the expense of elevated wake-up times for network-initiated data transfers.
In a packet based system, it is assumed that all resources are assigned more or less temporarily by the network to the UE by use of allocation tables (AT) or more general by use of a downlink (DL) resource assignment channel or a DL shared control channel. Reception of allocation tables is periodic and determined by the DRX period in use. The network will schedule possible resource allocations to the UE through AT which will be received by the UE at each DRX cycle. These assignments or allocations may be grouped into one-time allocations and persistent allocations. One-time allocations mean that the resources allocated to the UE in the received AT is valid only in the following sub-frame. The next allocation is then received through the next received AT. On the other hand, persistent allocation may assign allocation that may be valid for a predetermined period of time. This means that the allocations received may be valid, e.g., until next AT is received.
Consequently, DRX has direct impact on how often the network is able to address the UE. The need for the network to be able reach/address a UE depends on the connection type(s) between the UE and network. In case of a streaming connection, the DRX cycle will most probably be different than in case of a mail download. This is linked to the quality of service (QoS) of the connection.
As UE power consumption greatly depends on how often UE has to turn on its transceiver, it is clear from the above description that the DRX interval has impact on UE power consumption. This means that one key to power saving in Long Term Evolution (LTE) is to make it possible to optimize the use of DRX in such a way that the network always can utilize the longest possible DRX taking the connection restrictions into account.
Long DRX periods though will have negative impact on the data throughput in general as the networks capability to reach the UE decreases as the DRX interval increases. Long DRX will also impact the network packet schedulers possibility and flexibility to change the resources allocated to the UE. Limiting the packet schedulers possibility to change the resources used by a UE might have impact on the overall system in the way that the air interface resources are not used in an optimal way. Waste of air interface resources in a wireless system should minimized when ever possible as this is normally the most limited resource.
Thus, the DRX cycles control when the UE is reachable in general either for UL or DL resource allocation through the AT. It thus follows that longest possible DRX or DTX periods should be used in order to ensure good power saving possibilities for UE, while shortest possible DRX or DTX periods should be used in order to ensure good and fast throughput to and from the UE and allow for flexibility in the UE resource assignments, seen from network packet scheduler point of view.